Electric fuse



March 27, 1934.

w. c. CRIMMlNs 1,952,058

ELECTRIC FUSE Filed March 25, 1933 7 l la va y) Patented Mar. 27, '1.934

wiunni o.

ELECTRIC FUSE Crimmn, Chiuso, IIL, alllgnor to Thomas l1. Ferguson Application March 25, 1933, Serial No. 662,727

11 (o1. zoo-113) The present invention relates to electric fuses and has for its general object the production of a fuse which may be used over and over again many times before it need be discarded. In at- 5 taining this object I employ mercury'as a fuse link or conductor between rigid fusefcontacts or terminals and locate an expansion chamber in proximity-to the mercury. The mercury normally rests in a capillary bore or tube in the body of the -l fuse and when at rest in such capillary chamber electrically connects the fuse terminals. When the current through the fuse becomes abnormal so as to blow the fusefthen the mercury becomes heated and vaporized and passes into the expansion chamber. In said chamber it gradually cools l :and condenses upon the walls and forms itself into globules of diil'erent sizes,- the greater part 'of which are too large to pass from the chamber into the capillary tube. Any'of the mercury 20 which passes into thelatter tube is quite insui cient to complete the circuit between the fuse terminals. Thus the fuse is blown and the circuit remains open. In order to set the fuse for subsequent use it is necessary to return the mercury to the capillary bore or tube. To bring this about it is necessary to break the mercury up into particles which are small enough to pass into the capillary bore and form a continuous conducting body therein. In the embodiment of the invention shown this breaking up of the mercury is accomplished by simply removing the fuse from its socket and shaking it. In this way the fuse can be reset almost any number of times and thus used over and-over again. In conjunction with the mercurylink I also preferably employ a fuse link of rigid fuse metal in series with the mer-v cury link. In case the capillary passage becomes enlarged by repeated blowings oi the fuse and lthe amount of current passed by the mercury link is thereby unduly increasedi then the noniiuid metal link is relied n to interrupt the circuit. Ordinarily when latter fuse is blown the fuse hasnnished its life of usefulness, and is thrown'away.

Inprovidlnga fuseofthistypeldesirealso to have the saine emclent in operation, simple in construction. economical to manufacture and as durable as may be under the circumstances ot the the invention will be particularly the appended claims.

In said draW1n8. .Fig. l is a central longitudinal section through a fuse constructed and arranged in accordance with the present invention; Fig. 2 60 is a transverse section of the same, the plane of section being indicated by the line 2-2 of Fig. l; Fig. 3 is a partial central section similar to Fig. 1 illustrating the mercury in vaporized condition at the time the fusejblows; and Fig. 4 is a similar 65 section illustrating the mercury after the same has cooled and showing how the globules prevent a; reforming of the liquid fuse link. Throughout these views like characters refer to like parts.

Referring to said drawing in detail, 10 desig- 70 nates the outer body member of the plug structure. This member is preferably composed oi porcelain. It, however, may be composed of any other suitable insulating material; It is given the usual shape of a plug designed to lbe screwed into the usual socket. The outer circular wall of the member 10 is prvided with a series of threads 11 upon which the shell contact l2 is pointed out in threaded; The matter of applying this shell contact to the plug member may` be in accordance with any of the well known practices. The shell contact 12 is ordinarily threaded toagree with the threads 1l so that it may be readily screwed into position upon the member 10. The threads in the shell 12 are formed by the shaping of the 85 shell, as clearly illustrated.` The shell 12 in this way provides an outer screw thread .for screwing the plug into the socket as is well known.

The interior of the member 10 is provided with 90 a central tubular opening orbore 13'which is continuous from end to end of the plug except for a ledge 14 near the upper end of the bore. As shown-this ledge is triangular in cross section and extends inwardly from the walls of the bore 13. It is used as a support for the inner plug member or core 15. The latter is also composed of insulating material which is preferably bre or a' fibre compound of suitable composition to serve as an insulating part oi' the plug 100 structure. The upper end of the core 15 is preferably bevelled so asA to t against the under side oi' the ledge 14. When thus positioned,l its lower end is substantially flush with the lower 50 repeated Operations in service? end of the outer plug member 10. In order-.to 105 'rne :nu maire o f the invention wm b more fully understood upon reference tothe following secure the two plug members 10 and 15 together Va headed screw 16 is employed. 'I'his screw is detailed description taken in connection with the, accompanying drawing in which a preferred form 55 of the invention is illustrated. while the scope o f screwed into a threaded opening in the upper end of the core 15. This opening is part of "a central bore which extends throughout`the en- 11 tire length of the core 15. The upper portion 17 of vthis bore, as we shall see more fully hereinafter, constitutes the expansion chamber for receiving the mercury at the time the fuse is 5 blown. The screw 16 before being screwed into the upper end of the opening 17 is coated with a cement 18 of suitable composition to provide an air-tight connection so asy to hermetically seal the upper end of chamber 17. The screw 16 when screwed down against the upper end of the core 15 also engages the upper side of the auge 14. Thus'the screw 16 serves not only to hermetically seal the chamber 17 but it co,

operates with the upper end of the core `15 to clamp the same to the intervening ledge 14 and thus rmly secure-the core 15 in place in the outer plug member 10.

A screw 19 is threaded into a similar opening at the bottom of the core 15 and the threads of this screw are provided with a cement covering 20 so as to hermetically seal the lower endy of the lower portion 21y of the central bore through the core l5. The screw 19 is positioned so that its head extends beyond the lower of the body member l0 and the core 15, and in this way the screw 19 serves as the center conwhich the screw 22 may be passed into its threaded opening in the core 15. As clearly shown the screw 22, when screwed home, firmly secures the end of a fuse link 24 which is suitably apertured for the passage of the shank of the screw, the head of the screw firmly holding the end of the link in place. The outer end of the link 24 is soldered or otherwise connected at 25 to the shell contact 12. The fuse 24 is a strip of fuse material which is bent back and forth on itself as illustrated, and when in assembled position, occupies space within the recess 23. The screw 22 like the screws 16 and 19, is nrst coated with cement 26 before being screwed home, so as to hermetically seal the central bore through the core 15. As clearly shown when the screw 22 is in place it has a transverse opening 27 through it which is in line with the -upper portion 17 and the lower portion 2l of the bore. The diameter of the portion 27 is slightly larger than the diameter of the capillary bore 21 and considerably smaller than the diameter of the portion 17. The lower end of the bore 17 is beveled as indicated at 28 and thus provides an inclined wall leading from the wall of the portion 17 to the lwall of portion 27. In like manner there is a taper 29 at the lower portion of .the bore 27 as it enters the capillary bore 2l.

A body of mercury 30 fills the capillary bore 21 and the screw bore 27 and extends a short distancel into the expansion chamber 17. The amount of mercury used is sufficient to normally electrically connect the screws 19 and 22.. When the mercury is in normal position in the capillary tube 21, then obviously there is an electric circuit completed between the center contact 19 and the shell l2 which may be traced from contact 19 through the mercury 30, the screw 22 and. the fuse link 24 to the shell contact'12. Because of the small diameter given the capillary tube)21 it is possible when the mercury is in normal circuit closing position to move the plug structure about into sidewise, upside down and other positions without dislodging the mercury from its normal circuit closing position. Any mercury that may be moved by the handling of the plug will not be suilicient to interfere with the electric circuit between the screws 19 and 22.

However, as soon as the flow of current through the fuse, when in service, exceeds the amount for which the fuse is designed, then the mercury 30 will be heated and vaporized and promptly ejected into the expansion chamber 17 after the manner illustrated by the vapors 3l in Fig. 3. As soon as the mercury has been ejected into the expansion chamber 17, the circuit between the screws 19 and 22 will be interrupted. In other words, the fuse will be blown. As the mercury is received into the expansion chamber 17 it will strike against the walls of the chamber and be cooled and condensed and formed into globules, such as the globules 32 shown in Fig. 4. These yglobules will settle to the lower portion of the expansion chamber 17 but for the most part will fail to pass through the bore 2.7 into the capillary bore 21. If a few globules do pass into the latter bore they will be insufiicient to complete the circuit between the terminal screws 19 and 22. In this way the circuit will be kept open as long as the globules remain intact in the chamber 17.

It is possible, however, to agitate the globules in the chamber 17 and so reduce them in size that .they will pass down through the bore 27 into the bore 21 and form as a continuous mass again uniting the screws 19 and 22 to complete the normal circuit. l 'I'his agitation of the mercury in the chamber 1,7 might be produced in different ways but so far as the present disclosure goes, the agitation relied upon to put the fuse into normal circuit closed condition is that which is produced by removing the fuse plug from its socket and shaking it in the hand a few times. The shaking of the mercury breaks up the globules 32 and allows them to enter the capillary bore as previously explained.

When the fuse is rst'manufactured the fuse link 24 is given a slightly larger capacity than the capacity of the thread of mercury which lies in the capillary bore 21. However, should repeated operations cause the bore 21 to be enlarged by reason of the vaporizing of the mercury in it and the resulting deterioration of the adjacent walls' of the core 15 then the fuse link 24 may come into play. It will be obvious that as soon as the current which is allowed to pass through the'mercury reaches the capacity of the fuse link 24 then the latter will'be ruptured. When this point in the operation of the fuse is reached the fuse may be discarded. If desired the portion of the body member 10 adjacent to the upper end of the shell 12 at the point where the latter has they link 24 soldered to it, may be cut away as indicated at 33 so as to provide a peak-hole through which the condition of the link 24 may be inspected to determine its condition and whether or not the fuse should be discarded.

By setting the screws 16, 19, 22 in cement, the bores 21, 27 and the chamber' 17 are tightly sealed against the admission of air and thus the interior of the fuse is kept free from mercurous oxide and other objectionable products, thereby substantially increasing the life of the fuse. The shell 12 is usually composed of brass while the center contact 19 is composed or some goed conducting mate commonly copper. The screw 22 may be composed of different materials, preferably however a material should be used which will not amalgamate, such as iron, nickel, cobalt or the like, or alloys containing one or jxnore of these metals. Where iron is used as the material of the screw 22, then the diameter of the bore 27 through it should be about ten per cent (10%) greater than the diameter of the capillary bore 21. I! afcopper screw be used, then the diameter of the bore 27 should-be about fty per cent (50%) greater than the diameter ofthe bore 21. Ihis diierence is necessary because of the diii'erence in the readiness of the mercury to unite with Ithe two illustrative metals, iron and copper. For the diameter of the chamber 17, I'have found a diameter 'produced by a No. 29 drill about right.. -Such Ja,

diameter is about .136 oi' an inch. 'I'he diameterof the capillary bore 21 will be varied tofsuit the amperage at which themercury link will rupture the circuit. Thus, I have found in practice ,thatI diameters for diierent fuse values as follows are about right, namely:

` Fractions Amm oi an inch eases Elites It must be understood that inall these cases wherein particular dimensions are given, such dimensions are merely illustrative, as obviously other dimensions may be round equally as good in the case of fuses of diiierent capacities and diierent designs, and yet fuses and designs which come within the scope of the present invention. The

proportions illustrated in the drawing are sub-V stantially those of fuses which have been made and used with entire satisfaction.

Obviously, in carrying out the invention other changes and alterations than those indicated might be made. without departing from the spirit of the invention. I therefore do not wish to be limited to the details of the speciilc disclosure made herewith but aim to cover by the terms of the appended claims-all those changes and alterations which rightly come within the, spirit andscope of my invention.

I claim: l

1. An electric ruse comprising an outer body member of insulating material, a peripheral shell contact secured to the exterior of said outer body member, a core 'of insulating material positioned in a central bore formed in said body member, said body member having a ledge projecting -into said bore near its top, a headed screw screwed into the upper end of said core and cooperating with the upper end of said core` and with said ledge to secure said core in placein said body said transverse screw, the bottom of the larger portionI of said bore converging downward, the lower portion of said bore acting as a capillary tube to normally retain the mercury.

2. An electric fuse comprising an outer body of insulating material, a peripheral shell contact on the outer surface of said body, a central insulating member positioned in a central opening in said body, a central contact positioned at the lower end oi' saidC central insulating member, a transverse screw threaded into an opening in saidZM central insulating member,4 said body having a recess in one side in line with said transverse screw, a fuse link in said recess uniting said shell contact and said transverse screw, said central insulating member andl said transverse screw having a vertical bore comprising an upper portion o1' a given diameter and capacity and a lower portion Iof capillary diameter and less capacity, the intermediate portion or said vertical bore through said screw being of a diameter intermediate of those of said upper and lower portions,

and mercury normally iilling said lower capillary portion and electrically connecting said lower central contact and said transverse screw.

3. An electric fuse comprising an outer body of insulating material, a peripheral shell contact secured to the exterior of said body, 'a core of insulating material positioned in a central bore in said body, said body having a ledge projecting into said bore near its top, a headed screw screwed into a threaded opening in the upper end oi' said core, said ledge cooperating with the screw head and the adjacentend of the core to secure said core in place in said body, an electric terminal at the lower end of said core, a. terminal in said core at a point intermediate of the cores length. said body having a recess in its side in line with Said intermediate terminal, a fuse link in said recess electrically connecting said intermediate'terminal and said peripheral shell contact, and a body of mercury in a vertical capillary bore in said core, said mercury normaliy electrically connecting said lower and` intermediate terminals. the upper end of said bore communicating with an expansion chamber in the upper end of said core.

' 4. An electric fuse comprising an outer body of insulating material, a peripheral shell contact secured to the exterior of said body, a core of insulating material positioned in a central bore formed in said body, said body having a ledge projecting into said bore near its top; a headed screw screwed into a threaded opening in the upper end of said core, said ledge cooperating with the screw head and the adjacent end of the core to secure said core in place in said body, an electric terminal at the lower end oi' said core, a

terminal intermediate of said core connected electrically yto said shell contact, and a'body of mercury in a vertical capillary bore in said core, said mercury normally electrically connecting said lower and intermediate terminals, the upper. end of said capillary bore communicating 'with an expansion chamber in the upper end or said core. 5. An electric fuse comprising an outer body of insulating material, a peripheral shell contact on the outer surface of said body, a central insulating member positioned ina central opening in said body, a. central contactpositioned at the lower end oi said insulating member, a terminal in said Y insulating member at a point intermediate of its length, said outer body having a recess in its side in line with said intermediate terminal, a fuse link in said recess electrically connecting said intermediate terminal and said shell contact, and a body of mercury in a vertical capillary bore in the lower portion of said insulating member, said mercury normally electrically connecting said intermediate and lower terminals, the upper end of said bore communicating with an expansion chamber in the upper end of said insulating member. y

6. An electric fuse comprising an outer body 'of insulating material, a peripheral shell contact on the outer surface of said body, a central insu-, lating member positioned in a central opening in said body, a central contact positioned on the lower end of said insulatingmember, a terminal in said insulating member at a point intermediate of its length, said intermediate terminal being electrically connected to said shell contact, a fuse link included in said electrical connection between said terminal and contact, aand a body of mercury in a vertical capillary bore in said core, said mercury normally electrically connecting said lower and intermediate terminals, the upper endv of said bore communicating with an expansion chamber in the upper end of said insulating member. l

7. An electric fuse comprising a plug body composed of insulating material, a peripheral shell contact on the outer surface of said body, a screw threaded into the lower end of said body andconstituting the center contact of the fuse, a transverse screw threaded into a transverse opening near the middle of said body, said body having a recess in one side through which said transverse screw may be passed into said trans,- verse opening, a fuse link in said recess electrically connecting said transverse screw and said shell contact, said member having a vertical bore extending from end to end, the upper portion of said bore being of greater diameter than the lower portion thereof and having a volumetrical capacity several times that of said lower portion,

being of capillary dimensions so as'to normally retain the mercury therein. o

8. An electric fuse comprising a plug body composed of insulating material, a peripheral shell contact on the outer surface of said body, a screw threaded into the lower end of said body and constituting the center contact of the fuse, a middle screw threaded into a transverse opening insaidbody, saidbodyhaving arecessinone side in line with said middle screw, a fuse link in said recess uniting said shell contact and said middle screw, said body and middle screw having a vertical bore comprising alower portion ofA capillary diameter and given capacityand an upper portion of greater diameter and capacity, the intermediate portion of said vertical bore through said screw being of a diameter intermediate of those of said upper and lower portions,-

body and constituting the center. contact ofy the fuse, a terminal in said body at a point intermediate of its length, said body having a recess in its side in line with said intermediate terminal, a fuse link in'said recess electrically connecting` said intermediate terminal and said peripheral shell contact, and a body of mercury in a vertical capillary bore in said body, said mercury normally electrically connecting said lower and intermediate terminals, the 4upper end of said capillary bore communicating with an expansionchamber at the upper end of said 10. An electric fuse comprising a plug body composed of insulating material, a peripheral shell contact on the outer surface of said body, a screw threaded into the lower end of said body Vand constituting the center contact of the fuse,

an intermediate terminal mounted in said body and connected electrically to said shell contact, a fuse link included in said electrical connection between said terminal and contact, and a body of mercury in a vertical capillary bore in said body, said mercury normally electrically connecting said lower and intermediate terminals, the upper end of said capillary bore communieating with an expansion chamber in the upper portion of saidbody.

11. An electric fuse comprising a plug body composed of insulating material, a peripheral shell contact on the outer surface of said body, a screw threaded into the lower end of said body, and constituting the central terminal of the fuse, a terminal in said body at a point intermediate of its length, said bodvlhaving a recess in its side in line with said intermediate terminal, a fuse linkin said recess electrically connecting said intermediate terminal and said shell contact, and mercury in a vertical capillary bore in the lowerl portion of said insulating member, said mercury normally electrically connecting said intermediate and lower terminals, the upper end of said capillary bore communicating with an expansion chamber in the upper portion of said body.

12. An electric fuse comprising a plug body composed of insulating material, a peripheral shell contact on the outer slrface of said body, a screw threaded into the lower end of said body and constituting the central terminal of the fuse, a terminal in said body at a point intermediate'ef its length, said' intermediate tenninal being electrically connected to said shell contact. a fuse link included insaid electrical connection between said terminal and contact, and a body of mercury in a vertical capillary bore in said body normally electrically connecting said lower and intermediate terminals, the

upper end of said capillary Bore communicating chamber in the upper end with an expansion of said body.

13. electric fuse comprising a plug body of insulating material, shell and center contacts thereon, said body having a central bore consisting of a lower capillary portion and,an upper larger portion constituting a relatively large expansion chamber, a body of mercury normally occupying said lower capillary portion and contacting with said center contact, and means for uniting the upper portion of the normal mercury column to said shell contact, said means including an apertured contact member through the aperture of which said mercury is adapted. to extend whenever said mercury is in normal position in said lower capillary portion.

14. An electric fuse comprising a plug body of insulating material, shell and center contacts thereon, said body having a central bore consisting of a lower capillary portion and an upper larger portion constituting a relatively large expansion chamber, a body of mercury normally occupying said lower capillary portion and contacting with said center contact, means for uniting the upper portion of the normal mercury column to said shell contact, and a fuse link and other connections for electrically uniting the upper portion of the normal mercury column to said shell contact.

15. An electric fuse comprising a body, suitable external contacts on said body, said body having a capillary bore communicating with one of said contacts, conducting means leading from the other end of said bore to another of said contacts, and mercury normally located in said capillary bore and electrically uniting said contacts, said body having an expansion chamber communicating with said bore, into which chamber the mercury vapor is discharged from said capillary bore when the fuse is blown and in which chamber the mercury cools and forms` globules which will not pass back into said bore suliciently to again complete the normal circuit until the mercury is agitated, as by shaking, said conducting means including a transversely apertured member through the aperture of which said mercury extends whenever the same is in normal circuit closing position in said capillary bore.

16. An electric fuse comprising a plug body of insulating material, shell and center contacts thereon', said body having a central bore consisting of a lower capillary portion and an upper larger portion constituting a relatively large expansion chamber, a body of mercury normally occupying said lower capillary portion and contacting with said center contact, and means for uniting the upper portion of the normal mercury column to said shell contact, said means including in series connection a fuse link and an apertured contact member through the aperture of which saidmercury is adapted to extend whenever said mercury is in normal position in said lower capillary portion.

17. An electric fuse comprising a body, suitable external contacts on said body, said body having a capillary bore communicating with one of said contacts, conducting means leading from the other end of said bore to another of said contacts, and mercury normally located in said capillary bore and electrically uniting said contacts, said body having an expansion chamber communicating with said bore, into which chamber the mercury vapor is discharged from said capillary bore when the fuse is blown and in which chamber the mercury cools and forms globules which will not pass back into said bore sufliciently to again complete the normal circuit until the mercury is agitated, as by shaking, said conducting means including in series connection a fuse link and a transversely apertured member through the aperture of which said mercury extends whenever the same is in normal circuit closing position in said capillary bore.

WILLIAM C. CRIMMINS. 

